1. Technical Field of the Invention
This invention relates generally to wireless communication systems and more particularly to antennas used within wireless communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks to radio frequency identification (RFID) systems. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, RFID, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
Since the wireless part of a wireless communication begins and ends with the antenna, a properly designed antenna structure is an important component of wireless communication devices. As is known, the antenna structure is designed to have a desired impedance (e.g., 50 Ohms) at an operating frequency, a desired bandwidth centered at the desired operating frequency, and a desired length (e.g., ¼ wavelength of the operating frequency). As is further known, the antenna structure may include a single mono pole or dipole antenna, a diversity antenna structure, or any number of other electromagnetic properties. For instance, one popular antenna structure is a three-dimensional in-air helix antenna, which resembles an expanded spring. An in-air helix antenna provides a magnetic omni-directional mono pole antenna that is well suited for portable wireless communication devices. However, such an in-air helix antenna occupies a significant amount of space and the three dimensional aspects of it cannot be implemented on a planer substrate, such as a printed circuit board (PCB).
For PCB implemented antennas, the antenna has a meandering pattern on one surface of the PCB. Such an antenna consumes a relatively large area of the PCB. For example, for a ¼ wavelength antenna at 900 MHz, the total length of the antenna is approximately 8 centimeters (0.25 * 32 cm, which is the approximate wavelength of a 900 MHz signal). Even with a tight meandering pattern, the antenna consumes approximately 4 cm2. With the never-ending push for smaller form factors with increased performance, a PCB meandering antenna is not acceptable for many newer wireless communication applications.
Therefore, a need exists for a small form factor antenna that offers the benefits of an in-air helix antenna and the convenience of PCB fabrication without the above mentioned limitations.